1. Technical Field
This invention relates generally to accessories for mobile telephones, and more specifically to an apparatus for interfacing a mobile telephone with an existing audio system for hands-free use of the mobile telephone.
2. Background Art
Many cities and municipalities have recently passed ordinances restricting the use of cellular telephones while driving. For example, §588.03 of Westchester County, N.Y. states, “No person shall utilize a cellular phone while operating a motor vehicle on any public street or public highway within the County of Westchester.” Such laws generally include exceptions for cellular telephones equipped with “hands-free” devices. The Westchester code, for instance, states, “this law shall not be construed to prohibit a person operating a motor vehicle from utilizing a cellular phone equipped with a hands-free device.” Simply put, a hands-free device is any device or technological advance that allows the user of a cellular phone to utilize the cellular phone without holding it in his or her hand.
In response, manufacturers of audio accessories have developed different types of hands free devices. One example, as advertised on late night television, is a unit that includes a self-contained speaker that is coupled to the earpiece of the phone. In other words, the phone is held in a clamp and a microphone is positioned over the earpiece. When audio is emitted from the earpiece, the microphone senses the audio, amplifies it, and couples it to a two-inch loudspeaker disposed in the hands-free unit. When the user talks, the system relies on the microphone in the phone to pick up the user's voice.
The problem with this type of solution is that the audio is typically of poor quality. To begin, the hands-free microphone coupled to the phone's earpiece picks up much background noise. When this is amplified, the audio produced by the self-contained speaker is often distorted. Next, as the microphone in the cellular phone is designed for near-field use, it sometimes will not pick up the user's voice where the user is far away. Consequently, the transmitted audio from the cellular phone to the receiving caller can be very poor.
As most cars are equipped with high fidelity stereo systems, other manufacturers have found creative ways to employ the stereo loudspeakers in hands-free devices. For example, U.S. Pat. No. 6,163,711, issued to Juntunen et al., discloses a method of coupling a hands-free device to a stereo by modulating the telephone audio with AM or FM radio signals. When the hands-free device is coupled to the phone, the hands-free receives the audio signal and converts it to a FM signal that is, in turn, broadcast in the near field of the car stereo. The user simply turns to the preset “hands-free station” to hear the phone audio on the stereo loudspeakers.
The problem with this approach is two-fold: First, the FM signal broadcast by the hands-free unit is not localized to the car. Thus, if someone stops adjacent to the user at a red light, the other person may eavesdrop on the user's call by simply tuning to the proper radio station. Second, the user must physically tune the radio anytime a call is received. As anyone with an analog-tuning radio knows, this can be both time consuming and distracting.
A third approach is to couple the hands-free device between the stereo and the loudspeakers, as disclosed in U.S. Pat. No. 6,134,456 issued to Chen. In this system, a device is coupled between the stereo and the speakers. When a call is received, the device breaks the connection from the radio and makes a connection to the phone. The audio from the phone is then broadcast through the loudspeakers.
The problem with this system is that it is difficult to install. It requires that the power-carrying loudspeaker cable be severed and then reattached through the device. As loudspeaker wires often run through the sides and undercarriage of the car, this sometimes requires cutting of metal and plastic to reach the wires. The installation is almost always done professionally and is quite expensive.
There is thus a need for an improved hands-free device for cellular phones.